1. Field of the Invention
This invention generally relates to casks for transporting the nuclear fuel rods to or from nuclear power plant facilities and is specifically concerned with an improved basket structure for use in such a cask having shock absorbing former plates with improved heat transfer characteristics for protecting the fuel rods held within the basket structure.
2. Description of the Prior Art
Vessels for shipping the spent fuel assemblies produced by nuclear power plants are known in the prior art. Such vessels generally include a transportable steel vessel that is cylindrical in shape, and a basket structure that is receivable within the steel vessel for holding an array of rectangular storage containers. Each of these storage containers, in turn, may hold either a fuel rod assembly, or a consolidated fuel cannister. The general purpose of such transportable vessels is to provide a means for shipping spent fuel rods from a nuclear power plant to a permanent waste isolation site or reprocessing facility in as safe a manner as possible. At the present time, relatively few of such transportable vessels have been manufactured and used since most of the spent fuel generated by nuclear power plants is being stored in the spent-fuel pools of the reactor facilities. However, the availability of such on-site storage space is steadily diminishing as an increasing number of fuel assemblies are being loaded into the spent-fuel pools of such facilities every day. Additionally, the Nuclear Regulatory Commission (N.R.C) has been recently obligated (by way of an Act of Congress) to move the spent fuel assemblies from the on-site storage facilities of all nuclear power plants to a federally operated nuclear waste disposal facility starting in 1998.
While the transportation vessels of the prior art are generally capable of safely transporting spent fuel to a final destination, there is considerable room for improvement. Applicant has observed, for example, that no transportation vessel that he is aware of has any mechanism for absorbing mechanical shock applied to the sides of the vessel. This would constitute a substantial improvement, since many of the Zircaloy.RTM. tubes that form the outer cladding of the fuel rods are brittle and fragile as a result of both radiation degradation, and fretting against the grids of the fuel assembly during service. Hence, if any substantial mechanical shock is applied to the walls of such vessels, there is a substantial likelihood that at least some of the Zircaloy.RTM. fuel rods will crack or break completely, thereby spilling particles of the uranium oxide that forms the fuel pellets disposed within the Zircaloy.RTM. tubes. Dissipation of such radioactive particles within the vessel in turn increases the chances of exposing the personnel in charge of loading these spent fuel assemblies to potentially hazardous radiation. Still another area where such prior art transportation vessels could be improved is in the structure required to achieve integrality of the vessel and its contents after the vessel is loaded. The present mechanical structures necessary to eliminate all "slack" within the vessel interior are relatively complex, expensive to construct, and time consuming to implement. The elimination of such slack is completely necessary, since it is very important that the basket structure holding the fuel assemblies not rattle against the interior of the vessels during the transportation thereof. However, any simplified mechanism for eliminating the complex anti-slack structure must also have the ability to readily dissipate the residual heat generated by the spent fuel rods. Further, since the spent fuel assemblies are lifted directly out of the spent fuel pool as they are being loaded on such vessels, all components of the vessel must be completely drainable.
Clearly, there is a present and growing need for a transportation vessel that can safely and economically transport large amounts of spent fuel over interstate distances. Ideally, such a transportation vessel should be able to protect the relatively brittle and flimsy fuel rods contained within the fuel assemblies from cracking and rupturing in the event that the vessel is inadvertently exposed to mechanical shock.
It would be highly desirable if the transportation vessel and the basket structure contained therein could be easily and remotely assembled into a mechanically and thermally slack-free structure after the fuel assemblies are loaded therein, and easily and remotely disassembled after the fuel assemblies have been delivered to their final destination. Finally, the transportation vessel should have ample heat conductivity to effectively dissipate the heat generated by the residual radioactivity in the fuel rods.